module GovukPublishingComponents
  module Presenters
    # @private
    # Only used by the related_navigation component
    class RelatedNavigationHelper
      MAX_SECTION_LENGTH = 5
      DEFINED_SECTIONS = %w[
        related_guides
        topics
        collections
        topical_events
        world_locations
        statistical_data_sets
      ].freeze
      WORLD_LOCATION_SPECIAL_CASES = {
        "UK Mission to the European Union" => "uk-mission-to-the-eu",
      }.freeze

      attr_reader :related_navigation, :index_section_count

      def initialize(options = {})
        @content_item = options.fetch(:content_item) { raise ArgumentError, "missing argument: content_item" }
        @context = options.fetch(:context, nil)
        @related_navigation = related_navigation_contents
        @index_section_count = section_count
      end

      def related_navigation_contents
        case @context.try(:to_sym)
        when :sidebar
          {
            "related_items" => related_items,
            "related_guides" => related_guides,
            "collections" => related_document_collections,
          }
        when :footer
          {
            "topics" => related_topics_or_taxons,
            "topical_events" => related_topical_events,
            "world_locations" => related_world_locations,
            "statistical_data_sets" => related_statistical_data_sets,
            "related_external_links" => related_external_links,
            "related_contacts" => related_contacts,
          }
        else
          {
            "related_items" => related_items,
            "related_guides" => related_guides,
            "collections" => related_document_collections,
            "topics" => related_topics_or_taxons,
            "topical_events" => related_topical_events,
            "world_locations" => related_world_locations,
            "statistical_data_sets" => related_statistical_data_sets,
            "related_external_links" => related_external_links,
            "related_contacts" => related_contacts,
          }
        end
      end

      def section_count
        @related_navigation.select { |_, links| links.any? }.length
      end

      def construct_section_text(section, underscores_to_spaces)
        unless section == "related_items"
          defaults = [I18n.t("components.related_navigation.#{section}")]
          defaults << section.tr("_", " ") if underscores_to_spaces

          I18n.t(
            "components.related_#{@context}_navigation.#{section}",
            default: defaults,
          )
        end
      end

      def construct_ga4_section_text(section)
        # Force English so we can still understand what is being tracked if translated.
        underscores_to_spaces = true
        underscores_to_spaces = false if section == "related_content"
        I18n.with_locale(:en) do
          construct_section_text(section, underscores_to_spaces)
        end
      end

      def section_css_class(css_class, section_title, link: {}, link_is_inline: false)
        css_classes = [css_class]
        css_classes << "#{css_class}--#{@context}" unless @context.nil?
        css_classes << "#{css_class}--inline" if link_is_inline

        unless DEFINED_SECTIONS.include?(section_title) || link.fetch(:finder, false)
          css_classes << " #{css_class}--other"
        end

        css_classes.join(" ")
      end

      def section_data_track_count(section_title)
        String(@context || "sidebar") + String(section_title).camelcase
      end

      def section_heading_level
        @context == :footer ? "h2" : "h3"
      end

      def calculate_section_link_limit(links)
        links.length == MAX_SECTION_LENGTH + 1 ? MAX_SECTION_LENGTH + 1 : MAX_SECTION_LENGTH
      end

      def remaining_link_count(links)
        links.length - MAX_SECTION_LENGTH
      end

      def related_navigation?
        related_navigation.flat_map(&:last).any?
      end

    private

      def related_items
        related_quick_links = content_item_details_for("quick_links")

        if related_quick_links.any?
          related_quick_links + related_mainstream_content
        else
          content_item_links_for("ordered_related_items") + related_mainstream_content
        end
      end

      def related_world_locations
        content_item_links_for("world_locations")
          .map do |link|
            slug = WORLD_LOCATION_SPECIAL_CASES[link[:text]] || link[:text].parameterize
            link.merge(path: "/world/#{slug}/news")
          end
      end

      def related_statistical_data_sets
        content_item_links_for("related_statistical_data_sets", only: "statistical_data_set")
      end

      def related_taxons
        @related_taxons ||= content_item_links_for("taxons", only: "taxon")
      end

      def related_topics_or_taxons
        return related_topics if related_topics.any?
        return related_taxons if related_taxons.any?

        []
      end

      def related_topics
        @related_topics ||= begin
          mainstream_browse_page_links = content_item_links_for("mainstream_browse_pages", only: "mainstream_browse_page")
          topic_links = content_item_links_for("topics", only: "topic")

          return topic_links if topic_links.present? && mainstream_browse_page_links.empty?

          mainstream_browse_page_links + topic_links.find_all do |topic_link|
            mainstream_browse_page_links.none? do |mainstream_browse_page_link|
              mainstream_browse_page_link[:text] == topic_link[:text]
            end
          end
        end
      end

      def related_topical_events
        content_item_links_for("topical_events", only: "topical_event")
      end

      def related_contacts
        content_item_links_for("related", only: "contact")
      end

      def related_external_links
        content_item_details_for("external_related_links")
      end

      def related_mainstream_content
        return [] unless detailed_guide?

        content_item_links_for("related_mainstream_content")
      end

      def related_guides
        return [] unless detailed_guide?

        content_item_links_for("related_guides")
      end

      def related_document_collections
        content_item_links_for("document_collections", only: "document_collection")
      end

      def detailed_guide?
        @content_item["document_type"] == "detailed_guide"
      end

      def content_item_details_for(key)
        Array(@content_item.dig("details", key))
          .map { |link| { path: link["url"], text: link["title"], rel: "external" } }
      end

      def content_item_links_for(key, only: nil)
        links = Array(@content_item.dig("links", key))

        if key == "taxons"
          links = links.find_all { |link| link["phase"] == "live" }
        end

        if only.present?
          links = links.find_all { |link| link["document_type"] == only }
        end

        links.map do |link|
          {
            path: link["base_path"],
            text: link["title"],
            locale: link["locale"],
          }
        end
      end
    end
  end
end